1) Field of the Invention
The present invention relates to a unit supporting device and an image forming apparatus, and more particularly to a configuration for defining a positional relationship between a plurality of units and a member opposed thereto when each of the units is inserted into an accommodating position.
2) Description of the Related Art
In image forming apparatuses such as a reproducing machine, a printer, a facsimile machine, or printing machine, a record output can be obtained by performing a visualizing processing on an electrostatic latent image formed on a photoconductor, being a latent image carrier, by a developing device to transfer a-visualized image on a sheet or the like.
There are not only a configuration where a single photoconductor is provided for processing with only a single color, but also a configuration where a plurality of photoconductors are provided for forming an image for each plural colors. The latter case is used to form a multi-color image including a full color image.
For example, as a system for obtaining a full color image, there are a system that color images formed on respective photoconductors using developing agent such as toners with colors put in a complementary color relationship with colors for separating color are sequentially transferred on a conveying sheet in a superimposing manner and a system that, after color images on respective photoconductors are sequentially transferred on an intermediate transfer member, images transferred on the intermediate transfer member in a superimposing manner are transferred on a sheet in batch.
On the other hand, as one of configurations where a plurality of photoconductors are used, in the latter system of the systems, a configuration where photoconductors on which respective color images can be formed are arranged along a direction in which a belt serving as an intermediate transfer-member on which images are transferred from the photoconductors in a superimposing manner extends, so-called “tandem structure” is known (see, for example, Japanese Patent Application Laid-open No. 2001-281962).
In the image forming apparatuses, since part replacements and maintenance/inspection of respective devices used for image formation processing, so-called imaging devices, are conducted, such a configuration which the imaging devices can be pulled from their accommodating positions to their positions where they can be operated externally is employed.
In Japanese Patent Application Laid-open No. 2001-281962, a configuration for pulling out these devices to the positions where they can be operated externally is disclosed. Specifically, an image formation processing unit for each color is integrally configured of a unit having a developing device including a photoconductor used for image formation processing and a replenishing unit for such developing agent as toner used in the developing device and the like, and a unit including the photoconductor, a charging device, and a cleaning device. Such a configuration is employed that the image formation processing units corresponding to respective color are arranged in respective imaging stations and one image formation processing unit including a device to be replaced of these units is pulled out of the image forming apparatus main unit.
On the other hand, in such a tandem structure, there is a configuration provided with a transfer unit including a transfer belt as a transfer member passing through the imaging station. A configuration where the transfer unit approaches to and separates from the imaging station in order to avoid troubles such as jamming is proposed (see, for example, Japanese Patent Application Laid-open No. 2000-47450).
When images with plural color images are sequentially transferred, it is important to employ such a configuration that out of color registration is not caused by positional deviation between respective images in order to prevent image quality from being degraded.
In view of these circumstances, conventionally, such a configuration is proposed that positional deviations in superimposition among plural colors are prevented by shifting a movement amount of a photoconductor driving motor according to a deviation between a write timing on the photoconductor and a detection timing on a reference mark formed on a transfer member (see, for example, Japanese Patent Application Laid-open No. 2002-72607).
As the configuration for preventing out of color registration disclosed in Japanese Patent Application Laid-open No. 2002-72607, a mark detecting sensor supported by the image forming apparatus main unit so as to be opposed to the transfer member is used. However, in a configuration where the transfer unit including the transfer member approaches to and separates from the imaging station, as disclosed in Japanese Patent Application Laid-open No. 2000-47450, when the transfer unit can be inserted into and pulled out of a case of the apparatus main unit, there is a possibility that, when a positional relationship between the transfer member of the transfer unit inserted into the case and the mark detecting sensor deviates from a proper one, accurate control for preventing out of color registration cannot be achieved, as disclosed particularly in Japanese Patent Application Laid-open No. 2000-47450.
As the configuration for preventing out of color registration, there is the following configuration. A supporting leg fitted into an elongated hole formed in a side plate of the case to extend in a direction perpendicular to an inserting direction of the transfer unit is provided on a supporting stand for a writing unit, a supporting pin fitted into an elongated hole formed in a supporting portion of the case to extend along a direction parallel to the inserting direction of the transfer unit is provided on the supporting stand. In an insertion of the transfer unit into the case at an image forming time, a displacement of the supporting pin in a direction parallel to the inserting direction occurs, when the supporting leg positioned on the supporting stand for the writing unit is fitted into the elongated hole formed in the direction perpendicular to the inserting direction. The displacement is made possible in the elongated hole formed in the supporting portion of the case to extend in the inserting direction, so that positioning of the writing unit in the inserting direction and correction of inclination thereof are performed.
In this configuration, however, it is assumed that the supporting pin of the supporting stand for the writing unit is fitted into the elongated hole formed in the supporting portion for the case to extend in the direction perpendicular to the unit inserting direction in an upwardly moving course of the transfer unit from a downwardly moved position thereof. Therefore, it is necessary to conduct a positioning work after the transfer unit is once inserted instead of the positioning work conducted in the inserting course of the transfer unit, and an upwardly and downwardly moving mechanism for the transfer unit must be provided. In addition, the operation for positioning becomes complicated, and the entire configuration inevitably becomes complicated.
Furthermore, since the configuration for positioning has a fitting structure for the elongated hole, there is a possibility that positioning accuracy cannot be secured because of a working error between the elongated hole and a member to be fitted therein.
On the other hand, in order to solve a problem occurring when a mark detecting sensor or a writing unit is provided on the side of the case for the transfer unit that can be inserted into and pulled out of the case, for example, it is considered that the mark detecting sensor is provided on the transfer unit. In this case, it may be necessary to detach the mark detecting sensor disposed near the transfer member at a time of transfer member replacement, which results in complication of replacement work. In addition, since life-span of the transfer unit to be replaced and that of the mark detecting sensor do not coincide with each other, replacement of the mark detecting sensor whose replacement is not required is conducted at a time of transfer unit replacement, which results in running cost increase.
Since the mark detecting sensor is a constituent element or a part requiring a power supply, it is necessary to furnish a grounded power supply line through a harness or the like. However, when the harness is used, it may obstruct a work for inserting and pulling-out for the transfer unit. Furthermore, a space for wiring is required, which may result in deterioration of workability and structure complication.